1. Field of the Invention
The present invention relates to a method for writing data in a magnetic disk apparatus that employs a single surface of one disk of stacked magnetic disks as a dedicated servo surface, and a magnetic disk apparatus. In particular, the present invention pertains to a method for writing data in a magnetic disk apparatus that prevents the noise that occurs during data head writing from adversely affecting a servo head read signal, and a magnetic disk apparatus that employs that method.
2. Description of the Related Art
A magnetic disk apparatus, a kind of data storage device, includes rotary magnetic disks, magnetic heads, and an actuator to position the magnetic heads over desired tracks on the magnetic disks. In this magnetic disk apparatus, after the actuator position the magnetic head over a desired track on the magnetic disk, the magnetic head read data from or write data to the track. Such magnetic disk apparatuses are widely used as external data storage devices. Because of the recent emphasis on reducing the size of computer systems, compact magnetic disk apparatuses that have large memory capacities are in demand. To further expand the memory capacity of magnetic disk apparatuses, in addition to increasing the disk data recording density, it is also necessary to increase the number of disks that can be mounted in an apparatus without exceeding a predetermined height.
FIGS. 1A and 1B are explanatory diagrams for prior art.
As shown in FIG. 1A, a magnetic disk apparatus includes a plurality of rotary magnetic disks 10-1 to 10-n and an actuator (or a carriage) 12 that carries a plurality of magnetic heads 11-1 to 11-p at its extremity. When seeking a desired track, the actuator 12 moves the magnetic heads 11-1 to 11-p radially across the tracks on the magnetic disks 10-1 to 10-n. After the magnetic heads 11-1 to 11-p are positioned over the desired track, it performs either data reading from or data writing to that track.
To position the magnetic heads 11-1 to 11-p over a desired track, it is necessary to control the position of the actuator 12. For this purpose, a servo signal pattern, which has been recorded on one surface (servo surface) of a magnetic disk, is read by a servo head and the actuator 12 is controlled in consonance with the read servo signal.
Generally, a dedicated servo surface is provided either on the top magnetic disk of the stacked magnetic disks 10-1 to 10-n (magnetic disk 10-1 in the diagram), or on the bottom magnetic disk (magnetic disk 10-n in the diagram). When the thermal deformation of arms 13, of the actuator 12, to which are fixed magnetic heads 11-1 to 11-p, occurs, however, positioning differences between the servo head 11-1, which faces the servo surfaces and the data head 11-p, which is the farthest from the servo head 11-1, commonly occur. More specifically, the greater the distance between the arms 13, the greater is the temperature variation between the arms 13. Also, because the actuator 12 is not uniformly constructed, the thermal deformation of the arms 13 varies widely. Thus, there is an increased difference in the relative positions of the servo head 11-1l to the data head 11-p that is located farthest therefrom.
When the above described thermal deformation occurs at the actuator 12, the positioning difference (i.e., off track measurement) of the data head, located farthest from the servo head, increases with respect to the data track to which data was written by that data head before deformation, and read errors easily occur. Likewise, a data track where data was newly written after deformation has occurred tends to have a large off track measurement when the arm 13 assumes its original shape, and the above described conditions will also occur.
To prevent such an occurrence, one method reduces an off track measurement by providing a servo surface on a magnetic disk 10-m that is located almost in the middle of the stacked magnetic disks 10-1 to 10-n, and by shortening the distance between the top head and the bottom head, both of which are positioned the farthest from the servo surface.
In this method, as shown in FIG. 1B, a servo head 11-m, for the servo surface, which is positioned over the top surface of the magnetic disk 10-m, is collaterally paired with a data head 11-l, which is positioned over the bottom surface of the adjacent magnetic disk 10-l, with no intervening magnetic disk.
In this case, when the inter-disk spacing for the magnetic disks is reduced so that more magnetic disks can be stacked, because of the recently arising request for increased memory capacity, the space between the servo head 11-m and the data head 11-l is accordingly reduced. When data is written by the data head 11-l, therefore, electromagnetic induction caused by the write current that is supplied to the data head 11-l increases, and magnetic flux leakage from the data head 11-l greatly interferes with read signals from the servo head 11-m. Consequently, since electromagnetic noise leakage due to data writing by the data head 11-l is easily carried by the read output from the servo head 11-m, the quality of a servo signal is deteriorated and servo positioning errors easily occur.
For a magnetic disk apparatus within which the inter-disk spacing for the stacked magnetic disks is restricted, therefore, reduction of the electromagnetic noise is required in order to collaterally locate the data head 11-l with the servo head 11-m. Conventionally, the following proposals have been made:
(1) A shield plate is provided between the servo head 11-m and the collaterally positioned data head 11-l to prevent electromagnetic noise leakage (for example, Japanese Unexamined Patent Publication Nos. Sho 61-105783, and Hei 4-103088). PA1 (2) To reduce the effect on the servo head 11-m of the noise produced by its collaterally positioned data head 11-1, the relative positions of the two heads are altered by shifting them radially or circumferentially with respect to magnetic disks (for example, Japanese Unexamined Patent Publication No. Sho 63-53710). PA1 (3) In order to reduce noise, the points at which a write current that flows to the data head 11-1 rises and falls are shifted with respect to the peak of the output of a read signal from the servo head 11-m (for example, Japanese Unexamined Patent Publication No. Sho 58-97164).
As for the first proposal, however, shield plate components are necessary. Also, a shield plate attached to a servo head, or its collaterally positioned data head, alters the floating characteristics of the head to which it is attached compared to a head without an attached shield plate, and this causes excessive abrasion of a head and a magnetic disk. Further, because of the configuration of the apparatus, it is difficult to place the shield plate between a magnetic disk with a servo surface and a facing magnetic disk by adding it to the magnetic disk stack.
Regarding the second proposal, a gimbal to hold a magnetic head at the arm of a carriage cannot commonly be used for all the heads, and as the positions of these heads are shifted, the heads move off the tracks radially or circumferentially and narrow the movable range of a carriage.
Further, as for the third proposal, since the frequency of a write current is high even though the points at which a current rises and falls are shifted between the peaks of signals, noise leakage cannot be reduced. Therefore, it is not possible to prevent noise from being carried by a servo signal.